7 CREATING QUERY WITH QUERY WIZARD AND QUERY DESIGNER

Transcription

1 7 CREATING QUERY WITH QUERY WIZARD AND QUERY DESIGNER 7.1 INTRODUCTION Query is the most powerful feature of any database. A Query is a set of instructions in a logical order, required to produce the output based on Table(s) in a particular fashion. In FoxPro, as everything is a menu driven, queries can be designed just by clicking some options. Visual FoxPro also provides this feature to the users. It provides several query type depending upon whether you intend to just view data or update it as well. Query can be created based on complex conditions. In visual FoxPro, you can also define queries on local as well as remote data. 7.2 OBJECTIVES After going through this lesson you would be able to create query with Query Wizard create query using two Tables create query with Query Designer view query outputs

2 94 :: Computer Applications 7.3 CREATING A QUERY WITH QUERY WIZARD There are two ways of creating a Query using: (i) (ii) Query Wizard Query Designer To create a query with Query Wizard, choose New option from File menu or click the New tool. The New dialog box appears as shown in figure 7.1. Choose Query radio button and then click Wizard push button. Fig. 7.1: New Dialog box Visual FoxPro displays the Wizard Selection dialog box as shown in figure 7.2. The Wizard Selection dialog box provides options for creating several special purpose queries as well as ordinary visual FoxPro queries.

3 Creating Query with Query Wizard and Query Designer :: 95 Fig. 7.2: Wizard Selection Dialog Box The Cross-Tab wizard displays the data in Spreadsheet format. The Graph wizard displays a graph based on data from the FoxPro Tables. Select the Query Wizard in the Wizard Selection dialog box to display the Step-1 of the Query Wizard dialog box as shown in the figure 7.3. Fig. 7.3: Query Wizard Dialog Box

4 96 :: Computer Applications Selecting the Table The first step in creating a Query is to select the database table and fields on which your Query is based. In fact, the first dialog box of Query Wizard allows you to select one or more tables and select the fields of that table to include in the Query result. The Database and tables option available with the first step of Query Wizard dialog box displays the current database, if the database is open, otherwise, it displays the words Free Tables as shown in the figure 7.3. If a database is open, the names of the tables it contains appears in the scrollable list. If the database is not open, or if you want to use a Free Table, click the ellipsis button ( ), which opens a dialog box that allows you to select the required table. The table name occurs alone in the table list, if you select a Free Table Selecting the Fields After you select the Table from the table list you will notice that all the fields of the selected table are displayed in the Available Fields list. The Query Wizard dialog box includes a Field Picker buttons, which are found between the Available fields list and Selected Fields list. The arrow directions indicate the way they move fields. A single arrow moves a single field. Double arrow buttons move all the fields. To move a field from the available list, first select the field you want to move by clicking it or by using the arrow keys and then click the top buttons with right arrow. This moves the highlighted field to the selected fields list. Repeat this process to move more fields from Available Fields list to Selected Fields list as shown in figure 7.4. Fig. 7.4: Query Wizard with Select Fields

5 Creating Query with Query Wizard and Query Designer :: 97 If you want to move all the fields from Available Fields list to Selected Fields list, click the double right arrow button. If you have selected the wrong fields or if you want to remove any field from the Selected Fields lists, then you can select the field from the Selected fields list and click the left arrow button. Similarly, you can choose the double left arrow key to move all the fields from the Selected Fields list to Available Fields list. Remember that the order in which you select the fields for Query, the Query output will be shown in that order only. Choose Next push button to proceed to the next step of the Query Wizard Joining (Relating) the tables If you want to extract data from more then one table, you can go back to the Database/Table column to select a different table, and then click additional fields to include in the query. Remember that in such a query, you must define a relation for each additional table used in the query. The figure 7.4 shows the fields selected from the table STUDENT. If you specify fields from more than one table, then the Query Wizard move to step-2 of the Query Wizard. Here we have selected fields from one table, so step 2 is not required. The Wizard automatically skip the steps which are not required. In step 2 Relationship of Query Wizard dialog box allows you to define a relation between each table from which you selected fields. This step will be discussed in the next topic when we will discuss about creating query with two tables. Choose Next push button to move to the step 3 of the query wizard Filtering the data The Step 3 filtering of query wizard allows you to define filters. Filters mean defining conditional query. It limits the records included in the query by creating selection criteria or records in the source tables. The fields used for this selection may or may not be included in the query fields depending upon the fields you have selected for your query during the step-1 of the query wizard. For example, you might want the list of students from Jaipur; STUNDENT.ADD3 = JAIPUR To define the above expression in the Step 3 Filtering of query wizard as shown in figure 7.5.

6 98 :: Computer Applications Fig. 7.5: Step-3 of Query Wizard with Filtering Select STUDENT.ADD3 from the drop down list, select equals from the Operator list (default) and type JAIPUR in the Value text box. The following operators are available with the filtering: - Equals - Not equals - More than - Is Blank - Contains - In - Between The quotes around the strings are optional. However, case is important, if the selected operator is not Contains. Contains performs a case-insensitive test. Is Blank requires no strings in the value text box. To use the operator In, separate the values in the list with commas, but do add extra blank. For the operator Between type the first and last value separated with a comma, and not space.

7 Creating Query with Query Wizard and Query Designer :: 99 You can also define second filter criteria to use complete logical expression. Remember, you need to join the second filter to the prior one with either an AND or OR connector. The Wizard, however, limits you to just two filter conditions. To add more than two filter conditions you need to save the query and immediately modify it in the query Designer Specifying Sort Order The Step 4 Sort Order of query wizard allows you to create a sort order for the query result output. You can select any field from the available fields list. You can select more then one field for specifying the sorting order. Remember that the order in which you select these fields determines their sort priorities. You can also change the sort priorities by moving the selected field using the doubleheaded buttons to the left of the field names. Just click a doubleheaded button and drag it up or down to a new position. You can also send the data in ascending or descending order as per your selection of the Ascending or Descending radio buttons in the Step- 4 of the Query Wizard dialog box. Figure 7.6 shows the field selected i.e. Enrol and Name for the sort order. Choose Next push button to move further to the step-4 of the query wizard. Fig. 7.6: Step 4 of Query Wizard with Sort Order

8 100 :: Computer Applications Previewing the Query Result You can also click the Preview push button form the step 3, to run the Filtering of query wizard while still in the Wizard and view the results. The Browse window displays the records that match the expression as shown the figure 7.7 Fig. 7.7: Previewing the Query Result You can scroll through the window to make sure the conditional expression is finding the records that you actually want. If you do not get the expected result records, you can use the back button to return to any prior step and change the query definition. You can move between the Preview and any wizard step as many times as you like. Choose Next push button to proceed further in the query wizard after closing the Browse window of the Query Results Saving a query The last step of Query Wizard Step 5 Finish dialog box appears when you click Next push button from the Sort Field step-4 of Query Wizard as shown in figure 7.8. This last query wizard dialog box allows you to save the query with any one of the following three options: - Save query - Save query and run it - Save query and modify it in the Query Designer.

9 Creating Query with Query Wizard and Query Designer :: 101 Fig. 7.8: Saving a Query When you click Finish push button, Visual FoxPro Displays the Save As dialog box to type a name for the query. If you type the name as QRY-1 of your query then Visual FoxPro saves the query with this name and with extension name QPR, which stands for Query Program. Once you save the query, you can only modify it further by using Query Designer. INTEXT QUESTIONS 1. Write True or False for the following statements (a) (b) (c) (d) Query can only be viewing data and not updating data. The first step in creating a Query is to select the database table and fields. Query can be created using two or more tables. You can not preview the query result. 2. Fill in the blanks:

10 102 :: Computer Applications (a) (b) (c) In selecting fields, the fields are moved from field list to field list. You must define a for each additional table used in the query. Filters mean defining query. 3. Write steps for finding Students from Jaipur and Delhi in Table Students. 7.4 CREATING A QUERY WITH TWO TABLES USING QUERY WIZARD In the previous section you have learnt the queries using one table. Most databases contain several related tables. To learn how to create a query with two tables, let us create one more table named RESULT, with following structure and having one common field ENROL. To relate between two tables, both the data tables should have at least one common field. Structure of table: RESULT.DBF Field Field Name Type Width 1. ENROL C 9 2. SUBJECT C MARKS N 3 Now, add the following records to the table RESULT.DBF Record ENROL SUBJECT MARKS HINDI ENGLISH MATHS HINDI ENGLISH HINDI 34 Now, do the following steps to create a query with two tables STUDENT.DBF and RESULT.DBF using query wizard. 1. Choose New option from the File menu, select the Query radio button and click the Wizards push button. The Wizard

11 Creating Query with Query Wizard and Query Designer :: 103 Selection dialog box appears, click the Query Wizard button. This is similar to what we discussed in the previous section. 2. The Step-1 Field Selection of Query Wizard dialog box appear, when you click Query Wizard from the Wizard Selection dialog box. Click the right button of the Database/Tables control, to display the Open dialog box to add the STUDENT table to the list and then click this button again to add one more table RESULT which we have created. 3. Select the table STUDENT to display its fields in the Available Fields list. Now select the following fields from the Available Fields and move them to the Selected Fields list by double clicking them or by using the right arrow button. - ENROL - NAME Then select the table RESULT from the Database/Tables list to display the fields of RESULT table in the Available Fields list. Select the fields SUBJECT and MARKS to add them in the selected fields list as shown in the figure 7.9 Fig. 7.9: Query Wizard with Two Tables

12 104 :: Computer Applications 4. Click Next push button, Visual FoxPro displays the Step-2 Relationship dialog box of the Query Wizard. In this box you have to specify how the tables are related, as shown in figure Fig. 7.10: Relate Table of the Query Wizard It is suggested that the field STUDENT ENROL and RESULT ENROL has a common field ENROL in both the tables. Click the Add push button to display the relationship as shown in the figure Click the Next push button and the Step-2a Include Records of the Query Wizard dialog box appears. This dialog box allows you to include the records from the following options as shown in the figure a. Only matching rows b. All rows from the Table STUDENT c. All rows from the Table RESULT d. All rows from both tables

13 Creating Query with Query Wizard and Query Designer :: 105 Fig. 7.11: Query Wizard Include Records The default option is to include all records with matching records. 6. Click the Next push button and the Step-3 Filtering of the Query Wizard dialog box appears. If you want to filter the records of your query you can repeat the steps of Filtering as discussed in the previous section otherwise, you can skip this step by clicking Next push button again. Click the Next push button and Visual FoxPro displays the Step-4 Sort Order dialog box of the Query Wizard. Double click the STUDENT ENROL field to add it in the Selected Fields list as shown in the figure 7.12.

14 106 :: Computer Applications Fig. 7.12: Query Wizard with Sort Records 7. Click the Preview push button, to view the result of the Query, which includes the data form the two tables. Now click OK push button to close the Preview window. Lastly click the Finish push button from the step Finish and have the Query as QRY-2 in the Save As dialog box. Click Save push button from the Save As dialog box to save the Query. 7.5 CREATING QUERY WITH QUERY DESIGNER To create a query from scratch with Query Designer, choose New option from File menu. The New dialog box appears as shown in the figure Choose the Query radio button from the New dialog box and click the New File push button.

15 Creating Query with Query Wizard and Query Designer :: 107 Fig. 7.13: New dialog box to create a Query You can also use the query designer to modify a query, which you have created using Query Wizard. Choose Open option from the File menu and select the query file from the Open dialog box Adding a Table or View A query is always created on a table. If no table is in use, Visual FoxPro displays the Add Table or View dialog box, which lists all the tables of the open database. Fig. 7.14: Add Table or View

16 108 :: Computer Applications Figure 7.14 shows the Add Table View dialog box, where you can select a free table by choosing Other push button, which display the Open dialog box. It allows you to select a table from any directory or drive, including network drive. Figure 7.15 shows the table STUDENT.DBF that you have selected, is included in the panel at top of the Query Designer. The name of the table always appears in the window header. Fig. 7.15: Query Designer with One table Remember that you can also add table at any time, by choosing Add Table option from the Query menu or by clicking the Add Table tool from the Query toolbar to display the Add Table or View dialog box, which allows you to select a table. Similarly, you can also remove table at any time, by choosing Remove Table option from the Query menu or by clicking the Remove Table tool from the Query toolbar as shown in the figure 7.16.

17 Creating Query with Query Wizard and Query Designer :: 109 Fig. 7.16: Query Toolbar Field Panel After selecting the table STUDENT.DBF in the Query designer, you need to specify which fields you want to include in the query result. The Field panel of the Query Designer allows you to specify the fields you want to include in your query result. To specify fields in the Field panel, choose Fields tab from the Query Designer. The Fields Panel dialog box appears as shown in the figure To move the fields you want to include from the Available Fields list to the Selected Fields list, do one of the following: Select one or more fields in the Available Fields list that you want to use and choose Add > push button to copy them to the Selected Fields list. Double click on a field in the Available Fields list to copy it to the Selected Fields list. If you have to select all the fields, you can click Add All button. Similarly, if you have to remove any field, you can do by clicking Remove key or Remove All key. For example, let us choose the following fields from the Available Fields list by double clicking them. STUDENT.ENROL STUDENT.NAME STUDENT.FNAME STUDENT.COURSE STUDENT.ADD3 The selected fields are displayed in the Selected Fields list as shown in the figure 7.17 You can also include functions or expressions in the result, if you are creating a grouped query, by selecting them from the Functions/Expressions drop-down list and clicking Add push button.

18 110 :: Computer Applications Join Panel Fig. 7.17: Query Designer Fields selection This option is required when you are creating a Query with two or more tables. This option will be explained when we will discuss Creating Query with Query Designer using two Tables Filter Panel The Filter option in the Query Designer determines which records are extracted from the Table. If this option is empty, the query will extract all the records from the open table named STUDENT.DBF. To specify the Filter option to determine which records will be matched, select the Field Name drop down list to choose a field and Criteria list to choose the operator, and then enter the value you want to match the record in the data table as shown in the figure Choose STUDENT.ADD3 field name from the Field Name dropdown list and enter the text JAIPUR in the Example text box, to find all the records having Address3 as JAIPUR.

19 Creating Query with Query Wizard and Query Designer :: 111 Fig. 7.18: Query Designer with Filter Option Choose Run Query option from the Query menu, to run the query. The Browse window appears with all the records having Address3 equal to JAIPUR, as shown in the figure Order By Panel Fig. 7.19: Query Result of Filtering To specify the order in which records will appear in the query results, choose Order By panel from the Query Designer. The Order By panel occurs with all the fields in the Selected Fields list.

20 112 :: Computer Applications To specify fields that will determine the order of the query results, select a field from the Selected Fields list of Order By panel to determine the order of the query result as shown in the figure Fig. 7.20: Query Designer with Order By Panel You can also select more than one field to determine the order of the query results. Choose the Add push button to copy it to the Ordering Criteria list. Once you add Selected fields to the Ordering Criteria list, you can determine the order by choosing Ascending or Descending radio button. You can also adopt a shortcut method by double-clicking on a field from Selected Fields list to move directly to the Ordering Criteria list. To remove fields from the Ordering Criteria, select one or more fields from the Ordering Criteria list of Order By panel and choose the Remove push button, the selected fields no longer appear in the Ordering Criteria list or double-click on a field in the Ordering Criteria list to remove it directly from the Ordering Criteria list. The order in which fields appear in the Ordering Criteria list determines the order of priority of the query results.

21 Creating Query with Query Wizard and Query Designer :: 113 For example, double-click on the fields Student.Enrol, then Student.Name. This moves both the fields to the Ordering Criteria list and will affect the output to be sorted by Enrolment, plus Name as shown in the figure Choose Run Query option from the Query menu, to do the query. The Browse window appears in the ascending order, as shown in the figure Fig. 7.21: Browse window with Order By To save a query, choose Save As option from the File menu or click the Save tool. This opens the Save As dialog box to specify the name of the Query. Enter the name QRY3 in the text box and choose the Save push button as shown in the figure Fig. 7.22: The Save As dialog box

22 114 :: Computer Applications 7.6 CREATING QUERY WITH QUERY DESIGNER USING TWO TABLES To create a query with Query Designer using two tables, let us consider the two tables, which we have already created STUDENT.DBF and RESULT.DBF. Choose New option from the File menu. Visual FoxPro displays the New dialog box. Choose Query radio button and then choose New File push button. Visual FoxPro displays the Add Table or View dialog box to select the table for query. From the Open dialog box select the table named STUDENT.DBF. The Query Designer appears with the included table as shown in the figure 7.23 Fig. 7.23: Query Designer with Added Table at the top Choose Add Table option from the Query Menu. The Add Table View dialog box appears to select the second table. Choose Other option to display the Open dialog box, and select the table named RESULT.DBF You can either double-click the file name after highlighting it or choose OK. Visual FoxPro displays the Join Condition dialog box. By default,

23 Creating Query with Query Wizard and Query Designer :: 115 the first field STUDENT.ENROL will be displayed on the left and the second table RESULT.ENROL will be displayed on the right with a joining line as shown in the figure The Join Condition dialog box is displayed with the following option for Type of Join with its description given in the Description box: Inner Join Create a result set that includes only the Student records that match Result records. Left Join Create a result set that includes Student records and matching Result records. Right Join Create a result set that includes Result records and matching Student records. Full Join Create a result set that includes all Student records and all Result records. Fig. 7.24: Join Condition Dialog Box Select the Type of Join as per the requirement of the query and choose OK push button and close the Add Table or View dialog box. Please note that the expression you have created with Join Condition is displayed in the Join Panel of the Query Designer, and the two tables are connected with the to indicate the join, as shown in figure 7.25.

24 116 :: Computer Applications Fig. 7.25: Displaying the Join in the Query Designer Choose Fields panel of the Query Designer to select the fields for the query results. Select the following fields from the Available Fields list and move them to the Selected Fields list as shown in the figure Student.enrol Student.name Student.course Result.subject Result.marks Fig. 7.26: Query Designer with two tables

25 Creating Query with Query Wizard and Query Designer :: 117 Choose Run Query option from the Query menu to execute the query. The query result appears in the Browse window, as shown in the figure Fig Query Results using two tables To save the query you have created using two tables, open the File menu and choose Save option. The Save As dialog box appears and give the query name as QUERY-4 and click the Save push button. Similarly, you can create a query using more than two tables. 7.7 INTEXT QUESTIONS 4. Write True or False for the following statements (a) (b) (c) (d) To relate between two tables both the data table would have at least one common field. Include Records of the query wizard allows you to include only matching rows. You can add or remove table through Query Toolbar. You can not select more than one field to determine the order of the query result. 5. Fill in the blanks: (a) In order to create a query with query designer, choose radio button and click push button. (b) The name of the table always appears in the. (c) The extension name given to the query file is. 6. What are the four different types of Joins? 7.8 QUERY DESTINATION So far you have seen the query results in a Browse or Edit windows

26 118 :: Computer Applications on-screen. However, you may want to keep some query results for a longer time, perhaps saving them for future use or using them in a report. For this Visual FoxPro provides you with a feature Query Destination. To change the query destination from on-screen Browse window to a file or printer, choose the Query Destination option from the Query menu or by choosing Query Destination from the Query Designer toolbar. The Query Destination Dialog box appears as shown in the figure Fig. 7.28: Query Destination dialog box Visual FoxPro displays the following options from the Query Destination dialog box: - Browse - Cursor - Table - Graph - Screen - Report - Label 7.9 WHAT YOU HAVE LEARNT In this lesson you have learned about creating a query with query wizard and query designer. You have also learned how to create a query using two or more tables and how to join two tables. The principles of creating relationship between two tables are discussed in this lesson. You have also learned about viewing the query results and saving the query results using query destination.

27 Creating Query with Query Wizard and Query Designer :: TERMINAL QUESTIONS 1. What is the different steps involved in creating a query using two tables? 2. Explain the principles of relationship between the two tables. 3. What do you understand by query destination? 7.11 KEY TO INTEXT QUESTIONS 1. (a) F, (b) T, (c) T, (d) F 2. (a) available, selected, (b) relation, (c) conditional 3. as done in section 4.3.4, student.add3= JAIPUR and student.add3= DELHI 4. (a) Query, New File (b) (c) window header qpr 5. (a) Query, New File (b) (c) Database qpr 6. Inner, Left, Right and Full